Clutch plate facing



United States Patent Delaware No Drawing. Filed June 22, 1961, Ser. No. 118,758 3 Claims. (Cl. 162-155) This invention relates to friction plates and is particularly concerned with friction plates including facings of paper-like material thereon which plates are used in wet clutches and the like.

It is an object of this invention to provide a method for making paper-like clutch facing material for use in wet clutches wherein the fibers used in the making of paper are precoated with a rubber emulsion which protects the fibers against absorption of impregnants subsequently used in the paper.

In carrying out the above object, it is a further object to add a rubbery material in the form of an emulsion to the beater step in a paper-making process prior to the time the paper mat is made on the Fourdrinier screen whereby each fiber is coated coextensively thereover with a protective coating of latex emulsion. Thereafter, the mat is formed on the screen with a diatomaceous silica (calcined) addition and is calendered and heated for causing the rubbery emulsion to coat the fibers.

A still further object of the invention is to use latex in quantities of from 3% to 8% (solids) by weight of the fiber, as an additive, wherein the latex is of an average particle size of from 500-2500 angstroms and is carried by water in combination with a suitable emulsifying agent. In order to deposit the latex on the fiber particles, it is desirable to vary the normal pH of the solution of 7.0 or 7.5 and, in this respect, it has been found that, when the pH is about 5.0 the rubbery particles deposit on the fibers quite readily. This is accomplished by adding acids or acid salt solutions to bring the pH to the desired figure. A 10% to 30% alum solution may be used for this purpose.

Another object is to impregnate the latex treated sheet with a thermosetting resin wherein the sheet may be treated prior to or after attachment to a strong metal supporting member whereby, subsequent to the curing of the resin, a highly porous and strong friction facing is produced.

A further object is to provide a friction material wherein the coefficient of static and dynamic friction are about equal whereby a generally fiat torque curve is obtained which will yield relatively uniform torque response during the use of the clutch plate to which the paper material herein described is applied.

Another and important object of the invention is to use a butadiene acrylonitrile copolymer (Buna N) latex which whendispersed throughout the finished facing reduces and, in some cases, eliminates the tendency toward scorching of the facing during use thereof.

In application Serial .No. 27,492, filed May 9, 1960, one method of producing paper friction facings is disclosed. In this application, previously paper forming fibers are wax treated prior to resin impregnation thereof whereby greatly improved results are obtained from friction materials formed from said paper Without the wax, specifically where higher torque conditions are obtained and lower operating temperatures under such conditions prevail.

The present invention is directed to another and improved method for accomplishingthis end wherein additional benefits are obtained with finished facing material. In this invention, the paper pulp, for example, cellulose fibers, linen fibers, cotton linters, asbestos fibers, etc., either alone or in combination with friction fortifying or controlling materials, are treated with a Buna N latex in a beater and a latex emulsion,

prior to the manufacture of the paper sheet. This procedure results in greater uniformity since each fiber and particulate material is coated before the sheet is formed.

Specifically, the fibers used in the manufacture of the sheet with friction fortifying materials are added to water preferably a butadiene acrylonitrile copolymer having a butadiene to acrylonitrile balance by weight of about 5545, is added thereto. Specifically, from 3% to 8 %by weight (solids) of the latex may be added to the beater and the latex is caused to precipitate out upon the various fibers and particles by adjusting of the pH of the solution to about 5.5 to cause the emusion to break and the rubbery material to precipitate out upon the solid material. This may be accomplished by using a 10% to 30% by weight solution of alum in quantities sufficient to bring the pH of the solution from neutral (7.5) to about 5.5. Thereafter, the fibers coated with latex are sheeted out onto a conventional screen and are calendered and dried at temperatures above 212 F. to form a sheet of paper. During this drying step, the latex flows slightly to more or less coextensively cover the fibers. This sheet is next impregnated with a curable resin solution, for example, a phenol formaldehyde resin or phenol formaldehyde-butadiene acrylonitrile combination or any other suitable resin which is desired to be used. In this connection, any resin which will withstand the temperatures in the automatic transmission (not over 400 F.) and which is thermosetting in character may be used in accordance with the results desired.

After the paper is impregnated, and/or attached to supporting elements, the resin is cured at temperatures in the order of 300 F. to 375 F. for phenol-formaldehyde resin cement. During this curing step, the latex is believed to disperse or diffuse and at least partially coat the fibers and particles of the paper wherein each fiber is bonded to adjacent fibers by a strong resin-latex bond. Such a surface stabilizes the torque throughout the temperature range of operation and, in addition, reduces scorching of the facing during the slipping phase of clutch operation.

The Buna N emulsion may be used in combination with other latices if desired, for example, rubbery butadiene styrene copolymers (Buna S), rubbery polychloroprenes (Neoprene) etc., or in combination with waxes as disclosed in said aforementioned copending application Serial No. 27,492.

The frictional qualities of the facing material may be modified by the inclusion of rosin, guar gum, colloidal silica, mullite, crystabolite, etc. These materials with or without other friction modifying agents well known in the art may be added as indicated to obtain specific and desired performance requirements. I

Some examples of satisfactory recipes for use in the making of paper are as follows:

Buna N latex (67% butadiene-33% -acrylonitrile) 5 Example 2 Alpha cellulose fibers (short) 40 Diatomaceous silica (calcined) 15 Asbestos fibers 5 Ceramic or glass fibers 10 Red iron oxide 10 Cotton flock 16 Buna N latex (70% butadiene-30% acrylonitrile) 4 Example Alpha cellulose 63 Asbestos fibers (blue) 15 Diatomaceous silica (calcined) l5 Buna N latex (55% butadinee-45% acrylonitrile) 7 Example 4 Alpha cellulose 37 Blue asbestos fibers (crocidolite) 30 Diatomaceous silica (calcined) 20 Red iron oxide 1O Polychloroprene latex 3 Example 5 Blue asbestos (crocidolite) 9 Calcined diatomaceous silica powder (3-15 microns) 42 Cellulosic fibers 43 Buna N (55% butadiene45% acrylonitrile) 6 Example 6 I Mineral fiber 10 Diatomaceous silica (calcined) 42 Vegetable fibers 43 Buna N (5545 ratio) 3-8 In Example 6, as the Buna N latex addition varies, the difference may be adjusted for by varying any one or more of the remaining constituents, these variations all being dictated by the end results desired which are best determnied by trial in the specific device being used. As noted, the other important addition, namely the calcined diatomaceous silica, ranges from 15% to 45% by Weight of the whole. The variation in latex and silica additions will be dictated by performance requirements and are best arrived at by trial for the specific application. Cellulosic or vegetable fibers may include cotton linters, cotton rag stock, wood fibers, hemp, jute, flax, sisal, coroa, etc. either in bleached, semi-bleached or unbleached condition and further refined as desired. These may be augmented with inorganic fibers such as mineral wool, glass fiber, aluminum silicates, various types of asbestos, etc., together with synthetic fibers such as polyesters, polytetrafluoroethylene, vinylidene chlorides, polyamides, cellulose acetates, etc. and mixtures thereof.

In each of Examples l-6 the cotton linters or other natural fibrous materials are beaten well into a water slurry to form a 5% solid solution and are brushed together with the asbestos fiber or other mineral fibrous material and the diatomaceous silica earth and other friction fortifying material which should have a particle size ranging from about 2 to 15 microns. The Buna N latex is then mixed with the material on a dry weight basis of from 3% to 8% as required. Any waxes that are to be used should be added at this time in water emulsion form. The slurry is then adjusted to a pH of about 5 by the addition of an alum or other well known pH adjusting chemical. This will break the latex emulsion and cause adherence of the Buna N particles to the solid material in the slurry in a very uniform manner.

Thereafter, the paper is formed in a conventional manner on a Fourdrinier paper-making machine followed by drying'and calendering. This paper is next impregnated with the phenolic impregnant. A suitable phenolic impregnant may be made as follows:

P-arts Phenol crystals 47 Formaldehyde sol., 35 to 40 pct. tec 51.5 Ammonium hydroxide, 28 pct. sol 1.5

These ingredients are, of course, reacted into a reactable resin mixture. The impregnation of the paper discs may be accomplished by mixing equal parts of the above formulawith a suitable solvent such as isopropyl alcohol, to yield a solution having about 20% to 25% solids content after evaporation. The impregnation of the paper rings is accomplished by placing the rings in this diluted solution for from 2 t minutes, centrifugally spinning.

off excess resin and then drying the impregnated paper rings in an oven at about 200 F. for about 30 minutes. The resin may be applied to the paper by any other known method which yields a uniform impregnation, for example, transfer rolling, brushing, controlled spraying, etc.

After the discs have been dried, they may be cemented to metal discs by means of a suitable adhesion cement. One of such cements can be made by utilizing the resin ingredient disclosed in the above formula and diluting same with propyl alcohol together with a small quantity of hexamethylene-tetramine. The cement may be reinforced with china clay, if desired. While this cement is entirely satisfactory, other phenol formaldehyde base cemerits which are commercially manufactured, for example, phenol formaldehyde-butadiene acrylonitrile copolymer cements, sold under the trade name of Cycleweld, are also useful.

The cement is applied to the metal disc in a thickness of about .0005 inch. It is predried to a non-tacky condition which may be accomplished by short exposure to infrared heaters or other similar equipment. The impregnated ring is then placed on the cement coated metal disc and mechanically pressed thereto to remove air bubbles and is thereafter baked for about 20 minutes at 300 F. in circulating air to accomplish the bonding operation. This bonding operation may be carried out in stacks or with slight pressure on the discs to accomplish a satisfactory bond or, if the cement is first air dried, under slight pressure, the discs may be passed through a heating oven in a continuous fashion, all of such expedients being well known in the art. In all cases, it is understood that where pressures are used, these pressures are insufiicient to destroy the spongy nature of the impregnated disc and, in all cases, the particular impregnating and bonding resins are important only so far as they will withstand the temperature of operation of the device and provide strong bonds between the nonmetal friction discs and the metal supporting elements. As previously set forth, phenol formaldehyde base cements are highly satisfactory for these purposes. During the cure and bonding procedures, a loss in thickness in the order of 20% will occur due to the thermosetting qualities of the impregnant.

It should be understood that this disclosure is in no way limited to the specific ingredients used in the paper or the specific resin impregnants used. The invention is based upon the rubber emulsion treatment of the fibers to provide a paper having the same ingredients wherein the fibers are not so treated, and to the addition of the calcined diatornaceous silica. This material is spongy in nature and the calcining provides a surface layer of alpha chrystabolite on the surface of each particle. This abrasive material yields smoother action of the clutch plate whereby a smooth torque curve is obtained. This addition in conjunction with the latex dispersion offers a greatly improved material over prior art materials, and one which is heat resistant and smooth in its operation as a fluid type clutch pack.

While the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A clutch plate facing material for use in wet clutches and the like comprising a paper-like sheet adapted to be bonded coextensively to a metal supporting plate and having as its basic components, fibrous material taken from the class consisting of vegetable fibers, synthetic fibers and mineral fibers, together with a heat resistant phenolic binder and a friction fortifying addition consisting of calcined diatomaceous silica in combination with a rubbery latex.

2. A clutch plate facing material for use in wet clutches and the like comprising a paper-like sheet adapted to be bonded coextensively to a metal supporting plate and having as its basic components, fibrous material taken from the class consisting of vegetable fibers, synthetic fibers and mineral fibers, together with a heat resistant phenolic binder and a friction fortifying addition consisting of calcined diatomaceous silica in quantities of from 15% to 42% by weight of the whole in combination with rubbery latex solids in quantities of from 3% t0 8% by weight of the fibrous material used.

3. A clutch plate facing material for use in wet clutches and the like comprising a paper-like sheet adapted to be bonded coextensively to a metal supporting plate and having as its basic components fibrous material taken from the class consisting of vegetable fibers, synthetic fibers and mineral fibers, together with a heat resistant phenolic binder and a friction fortifying addition consisting of calcined diatomaceous silica in quantities of about 31% by Weight in combination With rubbery butadiene acrylonitrile latex solids of about 5% by Weight of the fibrous material used.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Hall: Diatomaceous Silica From Pacific Pulp and Paper Industry, April 1941, pp. 50, 51 and 53, 162-181 

1. A CLUTCH PLATE FACING MATERIAL FOR USE IN WET CLUTCHES AND THE LIKE COMPRISING A PAPER-LIKE SHEET ADAPTED TO BE BONDED COEXTENSIVELY TO A METAL SUPPORTING PLATE AND HAVING AS IT BASIC COMPONENTS, FIBROUS MATERIAL TAKEN FROM THE CLASS CONSISTING OF VEGETABLE FIBERS, SYNTHETIC FIBERS AND MINERAL FIBERS, TOGETHER WITH A HEAT RESISTANT PHENOLIC BINDER AND A FRICTION FORTIFYING ADDITION CONSISTING OF CALCINED DIATOMACEOUS SILICA IN COMBINATION WITH A RUBBERY LATEX. 